I found the best advice on my first darkside run was to just sit at the back and gain experience and just make sure you can make the entire ride without making them wait for you.
After the first ride you can gauge your strength and you know if you have it in your legs to do your share or just hang in for dear life next time you go out.
If you start to get tired hang on to the wheel in front and do everything you can to hold onto it. Once you lose the wheel you will struggle to get it back. Sitting in a slipstream when you are “bonked” is hard but its harder on your own.
don’t overdress, road riding is constant, no jelly beans enjoying the view etc. you will soon warm up.
above all, enjoy the burn